Natural cheese is generally made by adding a microorganism to milk which is capable of metabolizing lactose to produce lactic acid and develop acidity. The milk is usually set with a milk clotting enzyme, such as rennet, or by developing acidity to the isoelectric point of the protein. The set milk is cut, whey separates and is recovered from the resulting curd. The curd may be pressed to provide a cheese block and curing takes place over a period of time under controlled conditions. A product having flavor and body characteristics of natural cheese has been made by replacing at least a portion of the animal fat of the milk with vegetable fat and/or by replacing at least a portion of the casein of the milk with a vegetable protein.
It is well known to provide a product having some of the characteristics of natural cheese by grinding a natural cheese, and heating it with an emulsifying salt. The name given to the resulting product depends upon the ingredients used and its composition and, in some instances, is determined by Regulations promulgated by the U.S. Food and Drug Administration, known as Standards of Identity. For example, the term "pasteurized process cheese" refers to a product comprising a blend of cheeses to which an emulsifying agent, usually an emulsifying salt, and possibly acids, are added, the mixture is then worked and heated into a homogeneous, plastic mass. The moisture level of process cheese generally does not exceed about 44% and process cheese has a minimum fat level of about 40%, on a dry basis, under the Standards.
As used herein, the term "process cheese-type products" is intended to include those products known and referred to as "pasteurized process cheese", "pasteurized process cheese food", "pasteurized process cheese spread" and "pasteurized process cheese product". The term "process cheese-type products" shall also be deemed to include products resembling process cheese, process cheese food, process cheese spread and process cheese product, but which may not meet the Standards for any of the above products in that they contain ingredients not specified by such Standards, such as vegetable oil or vegetable protein, or do not meet the compositional requirements of such Standards. The term, process cheese-type products, shall be deemed to include any product, including but not limited to those referred to above, having the flavor and texture of a process cheese-type product regardless of the ingredients or manufacturing steps employed, and regardless of whether the Standards are met.
As indicated, presently known process cheese-type products may use a natural cheese or a cheese analog as a principal ingredient. The manufacture of natural cheese or cheese analog for these products can require extended curing times to develop the desired flavor. Generally, the amount of flavor developed is proportional to the length of time of curing and the extent of breakdown of the cheese. For instance, cheddar cheese which is cured for a relatively short period of time, e.g., 10 days, and which is referred to as "current cheese", has little cheese flavor or breakdown of the body; cheddar cheese which is cured from about 3 to 6 months, is referred to as "short hold cheese" and has increased flavor with increased body breakdown; and cheddar cheese which is cured for periods in excess of about 6 months and up to a year or more, is referred to as "long hold cheese" or "fully aged cheese", and has a high cheese flavor with more body breakdown. Process cheese-type products may comprise a blend of these cheeses to provide the desired flavor, body and texture to the final product. However, this method of manufacture of process cheese-type products makes it necessary to store cheese for substantial periods of time. Such storage is expensive and it would be desirable to provide a method for the manufacture of process cheese-type products in a much shorter period of time so as to avoid the need for any extended storage of cheese. Further, present methods of manufacturing process cheese-type products may require selection and proportioning of the cheese ingredients which requires special techniques and can result in flavor variations. It would be desirable to provide more consistent raw materials and manufacturing processes. Accordingly, many processes have been developed to produce natural cheese, a cheese base or a pre-cheese that is suitable for manufacture of process cheese.
It is also known that natural cheese can be manufactured using milk which has been subjected to membrane processing, such as ultrafiltration, to produce a retentate through removal of salts, lactose and water. Cheese making cultures are added to the retentate and the retentate is fermented, usually in the presence of a milk coagulating enzyme, such as rennet, to provide a coagulum. The resulting coagulum is cut or broken to cause syneresis resulting in whey separation. The whey is drained and the curd is processed. The type of cheese cultures used and the processing varies with the desired cheese product. The curd may then be salted, placed in molds and pressed to allow further whey drainage. The salting may be delayed until the curd is formed. The cheese is then ripened to the extent desired.
One of the shortcomings of the foregoing process utilizing a retentate and natural cheese processes, in general, is that serum protein and the portion of the cheese-clotting enzyme that is not utilized in the production of the coagulum is lost when the whey is drained. In the typical cheese-making process, more cheese clotting enzyme is added during the manufacturing process than is required to compensate for the loss of the enzyme in the drainage step. The presence of the milk clotting enzyme during the curing step serves to convert kappa casein to para kappa casein during curing of the cheese.
U.S. Pat. No. 4,820,530 to Moran, et al. describes a process for manufacture of a high solids cheese produced by fermenting and evaporating a milk retentate. The retentate is fermented to a pH above the isoelectric point without coagulation and the fermented retentate is spread on a surface under vacuum. Moisture is evaporated from the retentate under quiescent conditions to provide a curd having a total solids content of 55% or more. The curd is doctored off from the surface without substantially disrupting the curd structure and the curd is collected with minimum working of the curd and without substantial breakdown of the curd structure.
U.S. Pat. No. 3,988,481 to Coulter, et al. is directed to the preparation of cheese from milk which has been delactosed and dewatered by a process involving molecular sieving the milk to substantially separate and remove lactose and water soluble minerals from the milk to render the milk substantially sugar-free. Molecular sieving may be accomplished by gel filtration using a manufactured gel filtering agent, such as those sold under the tradenames Sephadex.TM. and BioGel.TM. or by electrodialysis or by reverse osmosis. The delactosed and partially demineralized milk product, containing principally protein in the form of casein and water and with or without fat is then concentrated to about 40-50% solids by removing water, as in a conventional vacuum evaporator supplemented by evaporation under vacuum in a swept surface evaporator or in a spray drier. A milk clotting enzyme is then added to the evaporated milk product and the resulting curd in the cheese-making mixture is then subjected to conventional manipulation to promote curd formation without any substantial syneresis. The resulting cheese is then molded.
The examples of the Coulter, et al. patent describe a laboratory procedure for preparation of skim milk colloid using a centrifugal Sephadex fractionation treatment, such as described by Morr, et al. in the Journal of Dairy Science, Vol. 50, No. 3, pp. 305-306 (1967). The technique of gel filtration with Sephadex G-75 and G-100 columns has been used to fractionate skim milk and whey proteins. This technique also separates the proteins from the low molecular weight components of skim milk, such as the lactose, amino acids, riboflavin and other soluble materials. The process described in the Morr, et al. article is an improvement of the Sephadex column method in that the separation into the fractions is accelerated by use of a centrifuge. The procedure consists of four major steps per cycle: (a) the sample is distributed evenly over the inside surface of the slowly rotating (60.times.g) Sephadex bed by means of a glass-tipped delivery tube leading from the sample container. (b) the rotor is rotated at 1,000.times.g for 10-15 minutes to spin the colloidal components of sufficient size to be excluded from the interior volume of the Sephadex gel. The colloidal components are drained continuously from the centrifuge head and collected in a number of separate fractions. (c) the rotor is slowed to 60.times.g and the Sephadex is eluted with up to two bed volumes of deionized water, to remove the lactose and other low molecular weight components contained in the interior volume of the Sephadex. The effluent is also drained continuously from the rotor and collected in a number of separate fractions. (d) the rotor speed is increased to a force of 1,000.times.g to spin out the excess eluant from the Sephadex and to prepare the bed for the next sample. The total time required for each complete cycle is approximately 30 minutes. The centrifugal Sephadex procedure for molecular sieving of milk is not suitable for large scale commercial manufacture of a delactosed milk fraction that could be used in the manufacture of cheese.
U.S. Pat. No. 3,899,596 to Stenne, dicloses a process for the production of cheese which comprises treating milk by ultrafiltration to obtain a product having at least some of the protein constituents of the milk, adding rennet to the liquid product after inoculation with suitable ferments, and introducing a batch of the renneted liquid into a vertical chamber in which it is left to coagulate. The coagulum is cut into slabs which provide the end product cheese.
U.S. Pat. No. 3,914,435 to Maubois, et al., also teaches cheese made from heat-treated milk and without conventional draining of whey by a process which involves ultrafiltering of the milk to produce a retentate and adding rennet to the retentate to cause coagulation to produce cheese curd and thereafter converting the curd into cheese.
U.S. Pat. No. 4,401,679 to Rubin, et al., discloses a process for preparing cheese base by concentrating milk through ultrafiltration, combined with diafiltration and evaporation, wherein the retentate from the ultrafiltration is inoculated with an acid culture before evaporation, and after evaporation, acidification proceeds to completion in packaging.
Cheese base material has been taught by evaporating moisture from retentate under turbulent conditions to provide a lower moisture concentrate. Such a process is described in an article by Ernstrom, et al. entitled "Cheese Base for Processing: A High-Yield Product from Whole Milk by Ultrafiltration", Journal of Dairy Science, Volume 63, pp. 228-234 (1980). The article describes a process wherein whole milk of normal pH, or acidified to a pH of 5.7, is concentrated by ultrafiltration to about 40% of the original milk weight and diafiltered at constant volume until a desired ratio of lactose to buffer capacity is established. Then, the retentate is further concentrated by ultrafiltration to 0% of the original milk weight. The retentate is then inoculated with cheese starter and incubated to completely ferment the residual lactose, pH control being achieved by controlling the level of lactose from the diafiltration step of the process. The product is further concentrated in a swept-surface vacuum-pan evaporator or a Luwa evaporator. It is pointed out that the use of a batch evaporator is necessitated when the retentate, upon fermentation, curdles or coagulates, since such a product cannot be readily processed in any continuous-flow evaporator.
PCT application WO 82/01806 to Jameson is directed to a process for producing cheese or cheese base containing substantially all the casein and whey proteins originally present in milk. In general, the PCT application discloses a process which permits efficient evaporation of water from fermented retentate. The process includes four steps: (1) selective concentration of milk to form a retentate; (2) increasing the ionic strength by the addition of salt, such as sodium chloride, to the retentate so as to maintain it in the liquid phase during fermentation; (3) fermenting the retentate; and (4) removing water from the fermented retentate to produce cheese or cheese base containing substantially all the casein and whey proteins originally present in the milk.
In the conventional making of cheese with rennet, the macro peptides formed by rennet action are lost in the whey with consequent reduction in yield and loss of milk protein material. It would be desirable to utilize the benefit of rennet action while avoiding whey removal with consequent loss of macro peptides.
Further, prior art methods for making cheese base materials at higher-solids with evaporation, in which evaporation is effected with high turbulence or the cheese base material is recovered with substantial working after evaporation, has resulted in destabilization of the higher-solids cheese base material, and a body and texture unlike various cheeses. This destabilization is particularly noticeable at total solids level in excess of about 60 to 62%, e.g., a cheese such as cheddar cheese, but is also present at a total solids level as low as 55%. Accordingly, cheese base materials heretofore produced by evaporating retentates to a total solids in excess of 60% generally have not provided the typical body and texture characteristics of high-solids natural cheeses.
The prior art teaches many different steps in respect to the manufacture of cheeses and cheese base materials from milk retentates. Much of the prior art is directed toward the manufacture of higher moisture or soft cheeses, and it has not been directed toward the production of high-solids natural cheeses from retentates.
It is a principal object of the present invention to provide a curd and a pre-cheese from a retentate by means of centrifugation techniques which is suitable for use in the manufacture of process type cheese.
It is a further object of the present invention to provide a pre-cheese which can be manufactured into a natural cheese.
It is another object of the present invention to provide a method for the manufacture of a pre-cheese and a natural cheese by a method wherein a milk clotting enzyme is added to a concentrate or retentate and the pre-cheese and natural cheese are made by a method which does not involve a subsequent whey drainage step.
These and other objects will become more apparent from the following detailed description and the accompanying claims.